Electronic component package and method of manufacturing same

ABSTRACT

An electronic component package according to the present invention includes a case ( 1 ) having a cavity portion containing an electronic component therein, and a lid member ( 8 ) fusion-welded to the case ( 1 ) via a fusion-welding layer ( 20 ) to close the cavity portion hermetically. The case ( 1 ) has a first metal layer ( 5 ) laminated on the case ( 1 ) in a manner to be exposed on the cavity open side. The lid member ( 8 ) has a core portion ( 9 ), and a second metal layer ( 10 ) laminated on a side of the core portion ( 9 ) facing the case ( 1 ). The fusion-welding layer ( 20 ) has a soldering material layer ( 12 A) formed of a soldering material, and first and second intermetallic compound layers ( 5 A) and ( 10 A), respectively, formed on opposite sides of the soldering material layer ( 12 A) as a result of diffusion of a major component of the soldering material into the first metal layer ( 5 ) and the second metal layer ( 10 ). The ratio of the area of the first and second intermetallic compound layers ( 5 A) and ( 10 A) in a longitudinal section of the fusion-welding layer ( 20 ) to the area of the longitudinal section of the fusion-welding layer ( 20 ) is in a range of from 25 to 98%. This package maintains superior airtightness even when exposed to a high-temperature atmosphere, which is higher than the melting point of the soldering material.

TECHNICAL FIELD

[0001] The present invention relates to an electronic component packagecontaining an electronic component therein.

BACKGROUND ART

[0002] Various electronic components, such as semiconductor devices,quartz crystal oscillators and piezoelectric vibrators, are oftencontained in respective electronic component packages in order for theelectronic components contained therein to be protected from externalenvironment.

[0003] As disclosed in Japanese Patent Laid-Open Gazettes Nos.2000-58687 and 2000-164746, there are known electronic componentpackages of the type comprising a case formed to define a cavity thatopens at the upper side of the case for containing an electroniccomponent, and a lid member fusion-welded to a peripheral edge surfaceof the case surrounding the opening defined at the upper side of thecase with a soldering material in order to close the cavityhermetically. The cavity defines an electronic component containingspace shutting out the outside world when the lid member isfusion-welded to the case to close the cavity.

[0004] As described in the aforementioned Gazettes, the lid member hasNi layers formed of Ni and laminated on opposite sides of a core portionformed of a metal having a low expansion coefficient such as Kovar.Various solder materials including, for example, Sn—Ag alloys, Bi—Agalloys and In—Sn alloys are usable as the aforementioned solderingmaterial.

[0005] The fusion welding of the lid member to the case is performed ata temperature equal to or higher than the melting point of the solderingmaterial. Generally, heating is conducted at a temperature 20 to 30° C.higher than the melting point of the soldering material for a relativelyshort time as short as some tens of seconds to minimize formation of abrittle intermetallic compound resulting from a reaction between thesoldering material-and an Ni-based metal.

[0006] An electronic component package containing an electroniccomponent therein is fixed at a predetermined position on a circuitboard by soldering, along with other electronic components. For volumeproduction and the like, a method of soldering different components to acircuit board at a time is usually employed, including: positioning thecomponents such as the electronic component package and other electroniccomponents on the circuit board; and passing the whole circuit boardthrough a heating furnace.

[0007] In this way the electronic component package is previously heatedfor the fusion welding of the lid member to the case containing theelectronic component with the soldering material and heated again forthe soldering of the package to the circuit board. When the solderingtemperature at which the electronic components are soldered to thecircuit board is higher than the melting point of the soldering materialused in the fusion-welding of the lid member, the fusion-welding portionbetween the case and the lid member is melted again to cause pinholes orcracks to take place at the fusion-welding portion, so that theairtightness of the electric component containing space in the packagelowers. If the airtightness of the electronic component package is to bemaintained high, there arises a problem that the soldering temperatureat which the package is soldered to the circuit board is limited to alow temperature, which is lower than the melting point of the solderingmaterial used for the fusion welding of the lid member, so thatsoldering materials that can be selected for use in the soldering to thecircuit board are limited also.

[0008] The present-invention has been made in view of the foregoingproblem. Accordingly, it is an object of the present invention toprovide an electronic component package having superior airtightnesseven exposed to a high-temperature atmosphere, which is equal to orhigher than the melting point of a soldering material used in the fusionwelding of a lid member.

DISCLOSURE OF INVENTION

[0009] An electronic component package according to the presentinvention comprises a case having a cavity portion containing anelectronic component therein, and a lid member fusion-welded to a cavityopen side of the case via a fusion-welding layer to close the cavityportion hermetically, the case having a first metal layer laminated onthe case in a manner to be exposed on the cavity open side, the lidmember having a core portion, and a second metal layer laminated on asurface of the core portion at the side facing the case, thefusion-welding layer having a soldering material layer formed of asoldering material, and first and second intermetallic compound layersrespectively formed on opposite sides of the soldering material layer asa result of diffusion of a major component of the soldering materialinto the first metal layer and the second metal layer, the ratio of thearea of the first and second intermetallic compound layers in alongitudinal section of the fusion-welding layer to the area of thelongitudinal section of the fusion-welding layer being in a range offrom 25 to 98%.

[0010] In this electronic component package the first and secondintermetallic compound layers of the fusion-welding layer interveningbetween the case and the lid member are formed by diffusion of the majorcomponent of the soldering material into the first and second metallayers and hence are irregularly and unevenly shaped with the solderingmaterial layer intervening therebetween in a involute condition. Sincethe first and second intermetallic layers of such a shape occupy 25 to98% of the fusion-welding layer, the fusion-welding layer is hard topeel off and, in addition, is less susceptible to pinholes or microcracks even at the time of re-solidification of the soldering materiallayer subsequent to re-melting of the soldering material layer at atemperature equal to or higher than the melting point of the solderingmaterial. For this reason, the electronic component package has superiorairtightness even when exposed to a high-temperature condition higherthan the melting point of the soldering material. If the area ratio ofthe first and second intermetallic compound layers is less than 25%, thearea of the first and second intermetallic compound layers of unevenshape is so small that the soldering material layer becomes re-melted inan extended region between the first and second intermetallic compoundlayers when re-heated, resulting in easy formation of such defects aspinholes. On the other hand, if the ratio is more than 98%, voids arelikely to result during the irregular growth of the intermetalliccompound layers so that cracks are formed as extending from such voidsin the intermetallic compound layers, resulting in the package havinglowered airtightness as in the former case. Further, the amount of thesoldering material sandwiched between the first and second intermetalliccompound layers is reduced and, hence, the fusion-welding layer, as awhole, becomes brittle and exhibits a lowered peel strength.Accordingly, the ratio of the area of the first and second intermetalliccompound layers in the fusion-welding layer is set to fall in the rangeof from 25 to 98%.

[0011] As described above, since the soldering material layer formedbetween the first and second intermetallic compound layers is shaped ina involute condition between the first and second intermetallic compoundlayers grown irregularly and unevenly by diffusion, the formation ofpinholes or cracks in the soldering material layer is unlikely even whenthe soldering material layer is re-melted by exposure of the package toa temperature equal to or higher than the melting point of the solderingmaterial and, hence, the electronic component package according to thepresent invention exhibits superior airtightness under a condition whereit is exposed to a high-temperature atmosphere.

[0012] In a preferred embodiment of the package according to the presentinvention, the first metal layer and the second metal layer are formedof pure Ni or an Ni-based alloy comprising Ni as a major component,while the soldering material layer is formed of an Sn-based solder alloycomprising Sn as a major component.

[0013] With the materials for respective layers thus selected, which areeconomical, an Ni-Sn-type intermetallic compound such as Ni₃Sn₄ can bequickly grown at a relatively low temperature, whereby the first andsecond intermetallic compound layers can easily be formed to thepredetermined ratio. Thus, the package is excellent in productivity. Inaddition, it is possible to suppress deterioration in thecharacteristics of the electronic component contained in the package dueto heating performed for the fusion welding.

[0014] In this case, use of a Pb-free Sn-based alloy as the Sn-basedsolder alloy is preferable. The use of such an alloy can avoidenvironmental pollution and detrimental influence upon human bodies dueto Pb.

[0015] In another preferred embodiment the fusion-welding layer isformed to have a mean thickness of from 10 to 50 μm. If the meanthickness of the fusion-welding layer is less than 10 μm, it is possiblethat local shortage of the soldering material occurs because ofundulation of the joined surfaces reflecting the working precision withwhich the lid member and the case have been worked. In such a case afusion-welding failure results. On the other hand, if it is more than 50μm, it is possible that an excess of the soldering material flows intothe case during the fusion welding to contaminate the interior of thecase. More preferably, the mean thickness of the fusion-welding layer isfrom 15 to 45 μm.

[0016] A method of manufacturing an electronic component packageaccording to the present invention comprises a preparatory process ofproviding a case formed with a first metal layer on a cavity open sideof a case body defining a cavity portion containing an electroniccomponent therein and a surface metal layer laminated on the first metallayer for facilitating fusion welding, and a lid member having a secondmetal layer laminated on one side of a core portion, and afusion-welding process of fusion-welding the lid member to the case. Thefusion-welding process includes superposing the lid member on the caseso that the second metal layer abuts on the surface metal layer of thecase via a soldering material, and holding the case and the lid memberunder heating to allow a major component of the soldering material todiffuse into the first metal layer and the second metal layer to formfirst and second intermetallic compound layers, which sandwich asoldering material layer formed of the remainder of the solderingmaterial. In the fusion-welding process the case and the lid member areheld under heating to form a fusion-welding layer comprising the firstand second intermetallic compound layers and the soldering materiallayer so that the ratio of the area of the first and secondintermetallic compound layers in a longitudinal section of thefusion-welding layer to the area of the longitudinal section of thefusion-welding layer assumes 25 to 98% after the fusion-welding processis completed.

[0017] In a preferred embodiment of this manufacturing method, the firstmetal layer and the second metal layer are formed of pure Ni or anNi-based alloy comprising Ni as a major component, while the solderingmaterial is formed of pure Sn or an Sn-based solder alloy comprising Snas a major component. The combination of these materials allows anSn—Ni-type intermetallic compound layer to be formed easily at arelatively low temperature by diffusion. In addition, it is possible tosuppress deterioration in the characteristics of the electroniccomponent contained in the package due to heating performed for thefusion welding. A Pb-free Sn-based alloy is preferable as the Sn-basedsolder alloy in terms of environmental protection and humans' health.

[0018] In another preferred embodiment, the case and the lid member arepressed against each other when they are held under heating. By so doingthe formation of voids can be suppressed, which results in thefusion-welding layer having improved soundness.

[0019] In yet another preferred embodiment, the case and the lid memberare heated at a temperature equal to or higher than the melting point ofthe soldering material to cause the soldering material to melt and thenheld at a temperature lower than the melting point of the solderingmaterial when the case and the lid member are held under heating. Withthis two-stage heating technique for the fusion welding, the firstheating at a temperature equal to or higher than the melting point ofthe soldering material causes the molten soldering material to contactsufficiently at once and adhere closely to the first and second metallayers. Subsequently, the growth of the intermetallic compound bydiffusion, which takes a long time, is allowed to proceed at arelatively low temperature lower than the melting point of the solderingmaterial and, hence, the first and second intermetallic compound layerscan be grown to a predetermined amount, while thermal damage to theelectronic component contained in the case is suppressed as much aspossible. For this reason the method is capable of manufacturing theelectronic component package of high quality.

[0020] In still another preferred embodiment, the fusion-welding layeris formed to have a mean thickness of from 10 to 50 μm in order to avoidthe occurrence of a fusion-welding failure and the contamination of theinterior of the case.

BRIEF DESCRIPTION OF DRAWINGS

[0021]FIG. 1 is a schematic sectional view showing an electroniccomponent package according to an embodiment of the present invention.

[0022]FIG. 2 is an enlarged sectional view of the fusion-welding layerof the electronic component package.

[0023]FIG. 3 is a schematic sectional view of a package assembly in astate before the fusion welding of a lid member.

[0024]FIG. 4 is a top plan view of a case used in the electroniccomponent package.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025] The inventors of the present invention have found that formationof a proper amount of an intermetallic compound, the formation of whichhas conventionally be considered to be inhibited as much as possible inthe fusion welding of a lid member, makes it possible to maintain theairtightness of a package even when the package is re-heated to atemperature higher than the melting point of a soldering material usedas well as to prevent deterioration in the peel strength of the lidmember. The present invention has been completed based on this finding.

[0026] Hereinafter, an embodiment of an electronic component packageaccording to the present invention along with a method of manufacturingthe same will be described in detail with reference to the drawings.

[0027]FIG. 1 shows an electronic component package according to anembodiment of the present invention, the package including a case 1containing an electronic component P in a cavity portion 3 thereof, anda lid member 8 fusion-welded to a peripheral edge surface of the case 1surrounding the opening of the cavity portion at a cavity open side ofthe case 1 via a fusion-welding layer 20 so as to close the cavityportion 3 hermetically.

[0028] The case 1 comprises a case body 2 formed of a ceramic materialand defining the cavity portion 3, a metallized layer 4 laminated on andunified with the peripheral edge surface on the cavity open side of thecase body 2 defining the opening of the cavity portion 3, and a firstmetal layer 5 laminated on and unified with the metallized layer 4. Themetallized layer 4 is formed of a high-melting-point metal such as W(tungsten) or Mo (molybdenum), while the first metal layer 5 formed ofpure Ni or an Ni-based alloy comprising Ni as a major component(hereinafter both referred to as “Ni-based metal”). The Ni-based alloyis an Ni alloy containing Ni in an amount of preferably not less than 20wt %, more preferably not less than 50 wt %, examples of which include80 wt % Ni—Fe, 80 wt % Ni—Cr, 65 wt % Ni—Cu, 45 wt % Ni—Fe, 42 wt %Ni—Fe, 36 wt % Ni—Fe, and 20 wt % Ni—Cu.

[0029] The lid member 8, on the other hand, has a second metal layer 10and a surface-protective metal layer 11, which are formed of theNi-based metal and respectively laminated on and unified with oppositesides of a core portion 9. The core portion 9 is formed of anFe—Ni-based alloy or Fe—Ni—Co-based alloy comprising Fe, Ni or Co as amajor component, such as Kovar, having a low expansion coefficient closeto the thermal expansion coefficient of the ceramic used as thepredominant material of the case 1. Examples of such alloys include anFe—Ni alloy having an Ni content of from 36 to 50 wt %, and an Fe—Ni—Coalloy having an Ni content of from 20 to 30 wt % and a Co content of 1to 20 wt %. The surface-protective metal layer 11 is laminated on theupper side of the core portion 9 in order to improve the corrosionresistance. The core portion 9 may be formed of a ceramic plate insteadof the Fe—Ni-based alloy or the like.

[0030] As shown in FIG. 2, the fusion-welding layer 20 interveningbetween the case 1 and the lid member 8 comprises first and secondintermetallic compound layers 5A and 10A formed integral with the firstmetal layer 5 and the second metal layer 10, respectively, and asoldering material layer 12A sandwiched between the intermetalliccompound layers 5A and 10A.

[0031] The soldering material layer 12A is formed of pure Sn or anSn-based solder alloy comprising Sn as a major component. The Sn-basedsolder alloy preferably contains Sn in an amount of 85 wt % or more andmay contain any other appropriate component, such as Ag, Au, Cu, Zn, Pb,Bi, Sb or the like, which can form eutectic or peritectic with Sn. Amongthese alloys, those of the type having an eutectic composition, such asSn-3.5 wt % Ag, Sn-10 wt % Au and Sn-0.7 wt % Cu, have low meltingpoints and are quickly meltable as a whole and, hence, are suitable forfusion welding at low temperatures. Taking environmental pollution anddetrimental influence on human bodies into consideration, Pb-freesoldering alloys are preferable.

[0032] The first and second intermetallic compound layers 5A and 10A areformed as a result of diffusion of Sn forming a major component of thesoldering material and Ni contained in the Ni-based metal forming thefirst and second metal layers 5 and 10 during the fusion welding of thelid member 8 to the case 1. For this reason, as shown in FIG. 2, thefirst and second intermetallic compound layers 5A and 10A areirregularly and unevenly shaped and the intervening soldering materiallayer 12A formed of the remainder of the soldering material is unifiedwith the first and second intermetallic compound layers in a involutecondition between them. In a longitudinal section of the fusion-weldinglayer 20 the ratio of the area of the first and second intermetalliccompound layers 5A and 10A to the overall area of the fusion-weldinglayer 20 assumes 25 to 98%, preferably 35 to 93%. The areas ofrespective layers in the longitudinal section of the fusion-weldinglayer 20 can be determined from color contrasts between the layers ofinterest in a composition image photograph of the section taken by EPMA.Image analysis software is useful in the calculation of the area of eachlayer.

[0033]FIG. 3 shows a package assembly in a state before the fusionwelding of the lid member, the lid member 8 being placed on the openupper side of the case 1. Though there are differences in theconstruction of the case before and after the fusion welding asmentioned afterward, like reference characters are given tocorresponding parts for convenience of description.

[0034] The case 1 in the state before the fusion welding, theconstruction of which is substantially the same as that of the stateafter the fusion welding to the lid member, is formed with a surfacemetal layer 6 of Au for example on the first metal layer 5 forfacilitating the fusion welding. Since a very small thickness issufficient for the surface metal layer 6, the surface metal layer 6 willbe melted into the molten soldering material and disappear during thefusion welding. For this reason the surface metal layer 6 is not shownin FIG. 1. The first metal layer 5 and the surface metal layer 6 areformed through plating.

[0035] On the other hand, the lid member 8, the construction of which isbasically the same as that of the lid member in the state after thefusion welding, has second metal layer 10 and surface-protective metallayer 11 respectively laminated on opposite sides of the core portion 9,and a soldering material layer 12 laminated on the second metal layer10. The soldering material layer 12 of the lid member 8 in a statebefore the fusion welding will diffusion-react with the first and secondmetal layers 5 and 10 to form the first and second intermetalliccompound layers 5A and 10A. Since the first metal layer 5 is absent inthe opening portion of the case 1, only the second intermetalliccompound layer will be formed in the corresponding portion as acorollary to the above. It is to be noted that the soldering materiallayer facing the opening portion of the case 1 in a state after thefusion welding is not shown in FIG. 1.

[0036] The lid member 8 is manufactured through a process including:pressure-welding a surface-protective metal layer forming material, acore portion forming material and a second metal layer forming materialtogether to form a laminate; and blanking the laminate thus obtained toa desired size. Since the second metal layer is sufficient to have athickness of about 5 μm, it may be formed through plating. In thisembodiment the soldering material layer 12 is formed integral with thesecond metal layer 10 of the lid member 8 by pressure welding. While thefusion-welding operability is improved by previously joining thesoldering material with the lid member 8, the soldering material neednot necessarily be unified with the lid member 8. In this case, it issufficient to place a lid member of a triple-layered structurecomprising surface-protective metal layer 11, core portion 9 and secondmetal layer 10 on the case 1 via a separately-provided solderingmaterial. Not only a thin-sheet soldering material but also a solderingmaterial paste comprising a soldering alloy powder mixed into a flux isusable as such a soldering material separately provided.

[0037] In the fusion welding of the package assembly, merely melting andsolidifying the soldering material is insufficient and it is requiredthat the intermetallic compound layers be grown to the predeterminedarea ratio by diffusion. To realize fusion welding accompanying adequategrowth of such an intermetallic compound the package assembly is usuallyheld at a temperature about 50 to about 250° C. higher than the meltingpoint of the soldering material for about 300 to about 1500 sec.However, some types of electronic components may be deteriorated intheir characteristics when they are held in a high-temperature conditionfor a prolonged time. In such a case it is desirable to employ such aprocess including: holding the package assembly at a temperature about10 to about 30° C. higher than the melting point of the solderingmaterial for about 10 to about 30 sec to melt the soldering material:after having allowed the molten soldering material to contact thesurfaces of the metal layers sufficiently, rapidly lowering thetemperature to a package-holding temperature ranging from a point about50° C. lower than the melting point of the soldering material to a pointjust short of the melting point; and holding the package assembly at thepackage-holding temperature for about 2 to about 20 hr to grow theintermetallic compound. This process makes it possible to obtain theintended fusion-welding layer 20 without deteriorating thecharacteristics of the electronic component contained in the package. Itis to be noted that the melting point of a solder alloy such as anSn-based solder alloy is equivalent to the eutectic temperature of thesolder alloy.

[0038] In the fusion welding it is sufficient to heat the packageassembly with the lid member 8 preferably positioned under the case 1.It is, however, desirable that the package assembly be intentionallypressurized so that the case 1 and the lid member 8 are pressed againsteach other. By so doing, the formation of voids in the intermetalliccompound during the fusion welding can be suppressed, so that thestability of fusion welding can be improved. It is possible to employ apressurizing method such as to place a weight on the package assemblyvia a presser plate formed of a material that does not react with thesurface of the package assembly, e.g. a ceramic material, or apressurizing method such as to bias the presser plate against thepackage assembly by means of a spring. The pressure to be appliedusually ranges from about 2×10⁻⁴ to about 1×10⁻² N/mm².

[0039] Usually, heating for the fusion welding is performed in a vacuumor in an inert gas atmosphere. The fusion welding in a vacuum or aninert gas atmosphere such as nitrogen gas makes it possible to preventthe electronic component from being oxidized by heating as well as toform an electronic component containing space provided with a vacuum oran inert gas atmosphere after the fusion welding. Thus, the electroniccomponent can be prevented from changing with time. Particularly wherean oscillator such as a quartz crystal oscillator is contained in thepackage, it is desirable from the viewpoint of improvement in resonancecharacteristic that the fusion welding be performed under vacuum.

[0040] Hereinafter, the present invention will be described morespecifically by way of examples to be described below. These examplesand the foregoing embodiments in no way are construed to limit the scopeof the present invention.

EXAMPLE

[0041] Cases were provided each having a W metallized layer (thickness:30 μm), an Ni layer (thickness: 15 μm) and an Au layer (thickness: 1μm), which had been stacked in that order on a peripheral edge surfaceof a case body formed of a ceramic at the cavity open side, theperipheral edge surface surrounding the opening of a cavity defined inthe case body. Lid members, which were separately provided, were eachsuperposed on the Au layer side of each case via a soldering material togive package assemblies. As shown in FIG. 4, each case was sized in topplan as follows: length A=4.1 mm, overall width B=2.6 mm, and widthC=0.35 mm, width C which is the width of peripheral edge surface 14 onthe cavity open side from the outer periphery of the case to the innerperiphery of the cavity portion. The planar size of each lid member wassubstantially equal to that of each case.

[0042] Each lid member had been manufactured through a processincluding: pressure-welding an Ni sheet (Ni layer forming material) ontoeach of the opposite sides of an Fe—Ni—Co alloy sheet (core formingmaterial) comprising 29 wt % Ni, 16 wt % Co, and Fe forming the balance;reducing the resulting laminate to a predetermined thickness bypressing; and blanking the reduced laminate to a predetermined planarsize. The lid member was of a triple-layered structure in which a Nilayer 5 μm thick was laminated with a core portion 80 μm thick on eachof the opposite sides of the core portion. As the soldering material,there was used an Sn-based soldering alloy sheet comprising 10 wt % Agand Sn forming the balance (eutectic point: 220° C.) or an Sn-basedsolder alloy powder of an eutectic composition comprising 3.5 wt % Agand Sn forming the balance (eutectic point: 220° C.). The Sn-basedsoldering alloy sheet was used as previously pressure-welded to a lidmember. The thickness of each of the resulting soldering material layersformed by the pressure welding is shown in Table 1. The Sn-based alloypowder was mixed with a flux to form a paste.

[0043] Each of the package assembly was placed on a pad plate with itslid member positioned under its case. For some package assemblies, aweight was placed on a ceramic plate set on each package assembly sothat a pressure of about 2×10⁻³ N/mm² worked on the fusion-weldingportion. The package assemblies were heated in a vacuum (0.1 Pa) or in anitrogen gas atmosphere (0.1 MPa). Table 1 also shows the fusion-weldingconditions. Samples Nos. 9 and 10 in Table 1 were packages eachmanufactured through a process including: holding the package assemblyat 240° C. for 15 sec to melt the soldering material; rapidly loweringthe temperature; and holding the package assembly at 200° C. for 10 hr.TABLE 1 Soldering Fusion-welding Pressurization Reflow Material LayerCondition Fusion- Performed: ◯ Performed: ◯ Sample Thickness Temperature° C. welding Not Performed: Not Performed: No. μm *Holding TimeAtmosphere X X 1 30 270*20 s Vacuum ◯ ◯ 2 30 270*20 s Vacuum X X 3 30320*800 s Vacuum ◯ ◯ 4 30 320*1200 s Vacuum X ◯ 5 20 200*5 hr Vacuum ◯ X6 20 425*800 s Vacuum ◯ ◯ 7 (Paste) 290*200 s Vacuum ◯ ◯ S (Paste)290*200 s Vacuum ◯ X 9 (Paste) 240*15s + 200*10 hr N₂ Gas ◯ ◯ 10 (Paste)240*15s + 200*10 hr N₂ Gas ◯ X

[0044] After the fusion welding, each package was vertically cut alongthe center of the length and the surface of the longitudinal section(taken on line X-X in FIG. 4) was observed by EPMA. A composition imagephotograph of the longitudinal section was analyzed with image analysissoftware to determine the areas of the first and second intermetalliccompound layers and the soldering material layer and the thickness ofthe fusion-welding layer. The image analysis software used wasImage-Pro, which is the commercial name of a product of MEDIACYVERNETICS.

[0045] Some of the packages having undergone fusion welding weresubjected to reflow (re-heating) by holding the packages at 260° C. for30 sec and then cooled for use as airtightness test samples. All thesamples were tested as to their airtightness in the following manner.Each of the samples was first placed in a hermetically-sealed vessel.After having reduced the pressure within the vessel to 0.1 kPa, thesample was pressurized with He gas at 0.5 MPa for about 2 hr to give asample to be evaluated. Then, the amount of He emitted from the samplewas measured with a He detector. A package having a measured value of1×10⁻⁹ Pa.m³/sec or less was considered to have permitted noinfiltration of He gas into the package, packages exhibiting this valueor less were regarded as passed the test. Further, the packages havingpassed the He gas detection test were immersed in fluorocarbon to checkwhether or not the generation of indiscrete gas bubbles occurred. Thosepackages which did not allow generation of indiscrete gas bubbles wereregarded as finally passed the test. The results of the observation aswell as the results of the measurement are shown in Table 2. TABLE 2Total Area of Area Fusion-welding Area of Soldering Intermetallic RatioLayer Airtightness Sample Material Layer: B Compound Layers: I l/(B + l)Thickness Passed: ◯ No. μm² μm² % μm Rejected: X *1  2053 326 13.7 31.0X *2  1256 366 22.5 21.0 ◯ 3 747 476 38.9 16.3 ◯ 4 894 326 26.7 16.3 ◯*5  1646 204 11.0 24.7 X 6 642 988 60.6 21.7 ◯ 7 195 1433 88.0 21.7 ◯ 822 757 97.1 10.4 ◯ 9 108 1087 90.9 15.9 ◯ 10  112 1463 92.8 21.0 ◯

[0046] As seen from Table 2, sample No. 1 having intermetallic compoundlayers, the area ratio of which did not meet the requirement of thepresent invention, exhibited airtightness deteriorated by reflow at 260°C. and hence was regarded as rejected. On the other hand, sample No. 2,which had not been subjected to reflow, exhibited satisfactoryairtightness though the area ratio of its intermetallic compound layersdid not meet the requirement of the present invention. Since sample No.5, which was subjected to a fusion-welding temperature lower than themelting point of the soldering material, did not allow a liquid phase toresult, the soldering material contacted the first and second metallayers insufficiently, with the result that the area ratio of theresulting intermetallic compound layers did not reach the predeterminedvalue in spite of prolonged heating. For this reason sample No. 5exhibited lowered airtightness. In contrast, samples Nos. 3, 4 and 6 to10 within the scope of the present invention, which were each formedwith intermetallic compound layers having an area ratio falling withinthe predetermined range, exhibited superior airtightness. It is to benoted that samples Nos. 1 and 2 as comparative examples were close tothe prior art but were subjected to a heating temperature higher thanthat according to the prior art.

1. An electronic component package comprising a case having a cavityportion containing an electronic component therein, and a lid memberfusion-welded to a cavity open side of the case via a fusion-weldinglayer to close the cavity portion hermetically, the case having a firstmetal layer laminated on the case in a manner to be exposed on thecavity open side, the lid member having a core portion, and a secondmetal layer laminated on a side of the core portion facing the case, thefusion-welding layer having a soldering material layer formed of asoldering material, and first and second intermetallic compound layersrespectively formed on opposite sides of the soldering material layer asa result of diffusion of a major component of the soldering materialinto the first metal layer and the second metal layer, the ratio of thearea of the first and second intermetallic compound layers in alongitudinal section of the fusion-welding layer to the area of thelongitudinal section of the fusion-welding layer being in a range offrom 25 to 98%.
 2. The electronic component package according to claim1, wherein: the first metal layer and the second metal layer are formedof pure Ni or an Ni-based alloy comprising Ni as a major component; andthe soldering material layer is formed of an Sn-based solder alloycomprising Sn as a major component.
 3. The electronic component packageaccording to claim 2, wherein the Sn-based solder alloy is Pb-free. 4.The electronic component package according to claim 1, wherein thefusion-welding layer has a mean thickness of from 10 to 50 μm.
 5. Theelectronic component package according to claim 2, wherein thefusion-welding layer has a mean thickness of from 10 to 50 μm.
 6. Theelectronic component package according to claim 3, wherein thefusion-welding layer has a mean thickness of from 10 to 50 μm.
 7. Amethod of manufacturing an electronic component package, comprising: apreparatory process of providing a case formed with a first metal layeron a cavity open side of a case body defining a cavity portioncontaining an electronic component therein and a surface metal layerlaminated on the first metal layer for facilitating fusion welding, anda lid member having a second metal layer laminated on one side of a coreportion; and a fusion-welding process of fusion-welding the lid memberto the case, including: superposing the lid member on the case so thatthe second metal layer abuts on the surface metal layer of the case viaa soldering material; and holding the case and the lid member underheating to allow a major component of the soldering material to diffuseinto the first metal layer and the second metal layer to form first andsecond intermetallic compound layers, which sandwich therebetween asoldering material layer formed of the remainder of the solderingmaterial, wherein in the fusion-welding process the case and the lidmember are held under heating to form a fusion-welding layer comprisingthe first and second intermetallic compound layers and the solderingmaterial layer so that the ratio of the area of the first and secondintermetallic compound layers in a longitudinal section of thefusion-welding layer to the area of the longitudinal section of thefusion-welding layer assumes 25 to 98% after the fusion-welding processis completed.
 8. The method according to claim 7, wherein: the firstmetal layer of the case and the second metal layer of the lid member areformed of pure Ni or an Ni-based alloy comprising Ni as a majorcomponent; and the soldering material is formed of pure Sn or anSn-based solder alloy comprising Sn as a major component.
 9. The methodaccording to claim 7, wherein the fusion-welding layer has a meanthickness of from 10 to 50 μm.
 10. The method according to claim 8,wherein the Sn-based solder alloy is Pb-free.
 11. The method accordingto claim 7, wherein in the fusion-welding process the case and the lidmember are pressed against each other when they are held under heating.12. The method according to claim 8, wherein in the fusion-weldingprocess the case and the lid member are pressed against each other whenthey are held under heating.
 13. The method according to claim 7,wherein in the fusion-welding process the case and the lid member areheated at a temperature equal to or higher than the melting point of thesoldering material to cause the soldering material to melt and then heldat a temperature lower than the melting point of the soldering materialwhen the case and the lid member are held under heating.
 14. The methodaccording to claim 8, wherein in the fusion-welding process the case andthe lid member are heated at a temperature equal to or higher than themelting point of the soldering material to cause the soldering materialto melt and then held at a temperature lower than the melting point ofthe soldering material when the case and the lid member are held underheating.
 15. The method according to claim 11, wherein in thefusion-welding process the case and the lid member are heated at atemperature equal to or higher than the melting point of the solderingmaterial to cause the soldering material to melt and then held at atemperature lower than the melting point of the soldering material whenthe case and the lid member are held under heating.
 16. The methodaccording to claim 12, wherein in the fusion-welding process the caseand the lid member are heated at a temperature equal to or higher thanthe melting point of the soldering material to cause the solderingmaterial to melt and then held at a temperature lower than the meltingpoint of the soldering material when the case and the lid member areheld under heating.